Radiant tubular heat exchanger



Aug. 2, 1960 E. NICKEL RADIANT TUBULAR HEAT EXCHANGER Filed Aug. 20,1957 2,947,288 7 Patented Aug. 2 1960 United States PatentOffice2,947,288 RADIANT TUBULAR HEAT EXCHANGER Eberhard Nickel, 'Stuttgart-Wa'ngen; Germany, assignor to Kohlenscheidungs-Gesellschaft,m.b.H., acorporationofGermany t. I

Filed Aug. 20, 19 57, 'Ser.No.67 9, 21ll 1 Claim. (01 122-418 5 Theinvention relates to a radiant tubular heat ex changer and isparticularly applicable to a heat exchanger 7 of the remaining heatenergy.

In steam generators of the above type having both superheaters andreheater in one furnace, difliculties are encountered when these steamgenerators are initially put on the line or when for operational reasonsthey are periodically shut down and againstarted up. These difficultiesarise out of the fact that when starting up a boiler of this type nosteam is flowing through the reheater tubes while these tubes areexposed to the high temperature of the combustion gases and aretherefore in danger of being damaged by overheating and burning.

Attempts'have been made heretofore to meet the above diificulties byarranging the reheater heating surface in gas passages behind thesuperheater so that the combustion gases produced in the furnace areinitially cooled by flowing over the steam generating and superheaterheating surfaces before they come in contact with the reheater tubes.The temperature of these gases is thereby reduced to a value which isnot much higher than'the' required reheat steam temperature. 7

However, in a steam generator in which the reheat vheating surface isdisposed in the manner'above described, a large amount of surface mustbe provided in the reheater because of the small temperature differen'cebetween the heating gases and the final reheat steam temperature.Because this large surface generally consists of high tempera-ture alloysteel tubing, the initial cost of a steam generator of thistypeis .veryhigh.

Furthermore, in cases where it is,required.that a reheat steamtemperature be obtained which is higher than the superheat'steamtemperature, the above described arrangement is not feasible, sinceit then becomes necesfill one.

The herein disclosed invention provides a novel apparatus which permitsthe starting up of a reheat steam generator without exposing thereheater to excessive gas temperatures and without incurring the abovedescribed operational disadvantages inherent in organizations heretoforeemployed for the solving of the problem.

It is accordingly the general object of my invention to arrange thereheaterheating surface within the furnace chamber in such a manner, inrelation to the superheater heating surface and the water wall heatingsurface, that the danger of overheating and burning of the reheatertubes is greatly reduced, if not eliminated, when starting up the boilerwithout the beneficial cooling effect of steam flowing through thereheater tubes.

With this and other objects in view which will become apparent from thefollowing description, reference is made to the accompanying drawingforming a part of this specification and illustrating my inventionwithout intention of limiting the invention to any particular form oruse. 1 Inthe drawing, Fig. 1 is a sectional side elevation of the steamgenerator incoi'porating my inventive improve- 'ments; v Fig. 2 is anelevational cross section taken along lines -.-2-2 of Fig. 1. I 'lReferring now to Fig 1 the illustrated steam generator comprises afurnace chamber F bounded by side walls 10, 12, -14 and 16 all of whichare lined with steam generating water wall tubes 18. These tubesoriginate in lower water-wall headers 19 and terminate in a steam andwater drum 20. This drum serves the purpose of collecting the generatingsteam and water mixture and also of receiving feed water from aneconomizer 21 by way of tubes 22 which line the rear wall 23 and roof24. The Water entering drum 2! flows downwardly through tubes 26 into anintermediate header 28 and through other connecting tubes 30 into lowerwater wall headers 19. Fuel and airyfor combustion is discharged intothe furnace chamber F by way of burners B. These burners in theillustrative embodiment hereof are located inor near the corners of thefurnace chamber F and are discharging fuel and air in directionstangential to an imaginary firing circle centrally located withinthe'fur nace chamber and produce a rotating column or stream of gasesrising within 'the furnace chamber towardsa furnace gas oiftake orgasfoutlet 32. A horizontal gas passage 34 adjoins the furnace gasoutlet 32 and leads into a vertical downward pass 36 having a horizontalgas duct 38 at its lower end through which the gases pa ss to an induceddraft fan 40 discharging the gases into the atmosphere by way of stack42. Economizer '21 is located in this vertical pass 36 and an air heater43 may additionally be employed to reduce the temperature of the gases.r i i The steam and water mixture delivered to drum 22' by tubes 18passes through avsteam and Waterseparator (not shown) located withindrum 20 for the separation of the steam from the water. The separated.steam leaves the drum by way of connecting tubes 44 to enter lowtemperature superheater section 46 located in horizontal gas pass 34,from whence the steam flows to' a high temperature superheater section48 located in'th e upper portion of furnace chamber F. superheater 48comprises a serise of tubular panels spacedly arranged within thecentral portion of the furnace chamber'F as shown in Fig. '2. t V Thesuperheated steam is heated to the desiredmaximum temperature insuperheater panels 48 from whence it flows through pipe 47 to the highpressure stag e'of a turbine A. After having given. up someof its energythrough loss in pressure andttemperaturefthe steam leaves that stage byway of pipe '49 to'entei and fiowtlirough low temperature reheatersection 50 from whence the partially reheated steam continues throughtube 5*). to enter the high temperature section 54 of the reheaterwherein the temperature of the steam is raised to the final reheattemperature. The steam thereupon flows through pipe 56 and passesthrough the low pressure stage of the turbine T where the major portionof the remaining the atmosphere until the steam pressure is sufiicientlyhigh to operate the turbine.

The present invention provides a most economical and novel solution tothe above problem by arranging the superheater heating surfacewithin acentral zone of the rising gas stream in the furnace,'and locating thereheater heating surface within a peripheral zone of the rising gasstream adjacent the water cooled furnace walls. In this manner the gasesin the center of .the gas stream, which are of a highertemperaturethan-the gases'passing along a peripheral zone because thelatter give up heat to the water walls, serve the. purpose ofsuperheating the steam in the superheater, and do not comeinacontactwith reheater heating surface whichat' thetime of initial operation isdevoid of cooling steam flow; In accordance with this inventionthereheater heating surface such as 54 of the illustrative embodiment isexposed to the peripheral gases which have been cooled by the water wallsteam generating tubes 18 covering the lower portion of the furnacechamber walls 14 and 16. Consequently the danger of overheating thesereheat tubes 54 is considerably minimized and the unit can be put on theline with greater safety and speed.

Furthermore, the invention provides novel facilities whereby thetemperature of the gases rising along the side walls and passing overthe reheater can further be reduced. This is accomplished in theillustrative embodiment of the invention by admitting relatively coolgases or air through a row of nozzles 60 provided in the'two opposing.side walls 14 and 16 which are parallelly disposed with respect to thereheater panels 54. These nozzles 60 are located directly below thelower portion of reheater'panels 54 as shown in Fig. 2. In accordancewith the invention the reheater panels 54 which are arranged adjacentthe water walls 14 and 16 are substantially shorter than the centrallylocated superheater panels 48 and the cooled gases are directed into apocket 53 formed by the outermost superheater panel and the side wallbelow the reheater tubes. A gas recirculating duct 62 is provided whichdelivers cooled gases from the outlet side of induced draft fan 40 tonozzles 60. A damper 64 in duct 62 permits control of the flow of theserecirculated cooled gases. These gases are discharged through nozzles 60in a direction towards the lower ends of the tubes of reheater panels 54as shown in Fig. 2. This permits additional cooling of the risingperipheral gas mass to which the reheater heating surfaces are exposedand further minimizes or even eliminates the danger of overheating ofthe reheater tubes at the time of the start-up operation of the unit.

Although the invention, as hereinabove described is used in'connectionwith a radiant steam generating-reheat unit, the invention can withequally beneficial results be applied to a radiant heat exchanger inconnection with a power plant wherein an other working medium than steamand water is used, such as air or other vapors, fluids, or gases.

While I have illustrated and described a preferred embodiment of mynovel organization it is to be understood that such is merelyillustrative and not restrictive and roof lined with heat-absorbingsteam generating water walltubes and having acombustion gas outlet atthe upper end of said furnace chamber; burner means for discharging fueland air -for burning into said chamber through the walls thereof atpoints remote from said gas outlet to produce a stream oflhot combustiongases flowing from said burner means through said chamber in heatexchange relation with said wall tubes for the generation of steamv andout through said gas outlet; superheating tubes 'for superheating saidsteam; said superheating tubes forming elongated upright panelsextending downwardly into said furnace chamber from said roof apredetermined distance, said superheater panels being spacedly arrangedwithin a central zone of said chamber and forming a horizontallyextending tube bank consisting solely of superheater tubes andmaintaining a predetermined space between the sides of said bank'andeach of said two opposing side walls; reheater tubes for reheating saidsuperheated steam, said reheater tubes forming elongated upright panelsextending downwardly into said furnace chamber from said roof asubstantially shorter distance than said predetermined distance, saidreheater panels being spacedly arranged for occupying said spaceprovided between each side of said superheater tube bank and saidopposing side walls, said reheater panels forming a tube bank consistingsolely of reheater tubes and forming a vacant pocket immediatelytherebelow which extends from each side of said superheater tube bank toeach opposing side wall; means for conducting recirculated cooledcombustion gases from a point downstream of said superheater tube bankin the gas flow sense to the furnace chamber at a location directlybelow said reheater tube bank; and means for introducing saidrecirculated gases into said vacant pocket provided between saidsuperheater tube bank and each opposing side wall, and immediately belowsaid reheater tube bank, whereby said reheater tubes are exposed to agas stream portion the temperature of which having been reduced by thecooling action of said water wall tubes, said extended superheater tubesand said recirculated gases to a greater extent than the temperature ofthe gas stream portion to which said centrally located superheater tubesare exposed.

References Cited in the file of this patent UNITED STATES PATENTS1,952,542 Ehlinger Mar. 27, 1934 2,685,279 Caracristi Aug. 3, 1954FOREIGN PATENTS 726,244 Great Britain Mar. 16, 1955

